At present, gas turbine engines employ annular combustors built-in between the compressor and turbine. In so doing, the combustor has usually no longitudinal split and the gas turbine engine is assembled by way of successive assembly of stator parts while mounting the vanes simultaneously or assembling the turbine rotors, and disassembled in an inverse sequence. This results in an increased consumption of labor during manufacture and, especially, during the servicing of the engine, inasmuch as access to the engine elements for inspection and repair is rather difficult.
Therefore, the designers' efforts are aimed at developing annular combustors having a longitudinal split in the plane of the split of other engine components. In this respect one of, main difficulties are offered by the flame tube of the combustor which is, affected by high temperatures, and whose design should satisfy the requirement of enhanced stiffness while ensuring the freedom of thermal expansion of its components inasmuch as the failure to meet this requirement results in the loss of shape by the flame tube, emergence of thermal stresses and, as a consequence, the warping of the flame tube components and the formation in the latter of cracks causing the failure of both the combustor and the entire engine.
Attempts at developing annular combustors with compensation for thermal expansion of individual components resulted in the combustor according to British Pat. No. 799,605.
This prior art annular combustor comprises a burner device located in the combustor inlet section and a flame tube formed by two concentric, outer and inner, shells.
The outer shell is split into sections in the longitudinal direction. Each section has, along the line of split, alternating projections and recesses, meshing with each other upon the assembly of the shell to form a movable joint serving to partly compensate for thermal deformation of the combustor in the circumferential direction. In a large-size combustor, however, the outer shell lacks stiffness, which is characteristic of combustors of stationary gas turbine engines. This affects the reliability of operation of the combustor and of the entire gas turbine engine.
Also known in the art is another annular combustor for a gas turbine engine, whose design helps facilitate the assembly and maintenance of the engine due to a longitudinal split of the combustor whose plane coincides with that of the engine split (cf., Trudy Uralskogo turbomotornogo zavoda "Opyt sozdaniya turbin i dizelei"--Proceedings of Uralskii Turbine Engine Works on the "Turbines and Diesels. Design and Manufacturing Experience," No. 2, 1972, pp. 88-94).
Said latter prior art annular combustor includes a front burner device secured in the inlet section of the combustor and a flame tube formed by two concentric, outer and inner, shells with curvilinear surfaces. Each one of the shells is split into sections in the longitudinal direction, the places of split being sealed with sealing members in the form of two plates. The first one of said plates, a flat plate, is attached to one section with its one end and, with its other end, rests freely on another section. The other one of said plates is attached with its one end to the section on which the first plate rests freely and, with its other end, envelops the latter to form therewith and with the section a sliding mortise joint. For joining the sections of the outer and inner shells in the combustor inlet portion, provision is made of a load-bearing arrangement in the form of a massive frame having a longitudinal split and including several massive rings, at least one of which embraces the sections of the outer shell while at least one other ring embraces the sections of the inner shell. The rings are rigidly interconnected with ribs of which two, arranged at a longitudinal horizontal plane in each half of the frame split, form the split flange while part of the other ribs are used for fixing the frame in the engine casing.
For joining the sections of the outer and inner shells in the combustor outlet section provision is made of single load-bearing rings likewise fixed on the engine casing. In this manner, the load-bearing arrangement in the form of a circular frame and the load-bearing rings are rigidly secured on the engine casing to form an integral rigid system.
Upon the combustor operation, especially, under unsteady conditions, a considerable temperature difference is observed between the circular frame and shell sections, which results in the emergence of temperature expansions of the sections relative to each other and to the frame. Each section is secured in the rings having an annular groove by means of a bracket. Due to the rigid attachment of the frame and single load-bearing rings to the engine casing, the annular groove and brackets, simultaneously serve to compensate for temperature expansion in the radial, circumferential and longitudinal directions. Therefore, this attachment is rather complicated and practically fails to accomplish a reliable operation of the combustor due to the absence of necessary expansion gaps, which results in the emergence of thermal stresses causing the warping of the combustor, for example, in the inlet section thereof, and the loss of shape.